The paper bases itself on recent theoretical writings in growth economics that empha-size the effects of both own R&D efforts and of interregional technology spillovers on regions´ productivity. We propose robust estimation techniques to evaluate the R&D spillovers across West German functional regions during the period 1976 - 1996. The findings suggest the existence of knowledge spillovers across functional regional boundaries. Moreover, significant spillovers are mainly found among geographically close regions. This finding confirms the hypothesis that proximity matters.